Lubricant for use in a wellbore

ABSTRACT

The present invention provides methods and apparatus for reducing friction and preventing galling between surfaces in a wellbore. In one aspect of the invention, a titanium carbide is disposed between surfaces of an expansion tool and a tubular to be expanded. The titanium carbide coating acts as a lubricant to reduce friction and prevent galling therebetween.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to lubrication of components for use in a wellbore. Particularly, the invention relates to reducing friction encountered during operation of a downhole tool in a wellbore. More particularly, the invention relates to the lubrication of wellbore components with a carbide material having a spherical grain structure. More particularly still, the invention relates to lubricating an expander tool with titanium carbide.

[0003] 2. Description of the Related Art

[0004] Galling of wellbore components due to friction has always been a problem in wellbore operations. Galling is surface damage to mating, moving, metal parts due to friction between the parts. In a wellbore, galling can take place between moving parts of a single component, like slips and cones of a packer or between a component and some other surface in the wellbore that is necessarily contacted as a component operates. Soft metals are more susceptible to galling than hard metals, and similar metal surfaces are more prone to galling than dissimilar metal surfaces.

[0005] Galling may occur when expanding tubulars in a wellbore. Expansion technology enables a tubular to be expanded and its diameter to be increased in a wellbore. Using this method, a liner, for example, can be hung off of an existing string of casing without the use of a conventional slip assembly. Tubulars can be expanded with a swedge or tapered cone that is physically pushed through the inside of the tubular with enough force that the inside diameter of the tubular is increased to at least the outside diameter of the cone. More recently, expander tools are fluid powered and are run into a wellbore on a working string. The hydraulic expander tools include radially extendable rollers which are urged outward radially from the body of the expander tool and into contact with a tubular therearound. As sufficient fluid pressure is generated upon a piston surface behind these rollers, the tubular is expanded past its point of plastic deformation. By rotating the expander tool in the wellbore and moving it axially, a tubular can be expanded along a predetermined length in a wellbore.

[0006]FIG. 1 is an exploded view of an exemplary expander tool 100 for expanding a tubular (shown as 200 in FIG. 2). A tubular is expanded by an expander tool 100 acting outwardly against the inside surface of the tubular. The expander tool 100 has a body 102 which is hollow and generally tubular with connectors 104 and 106 for connection to other components (not shown) of a downhole assembly. The connectors 104 and 106 are of a reduced diameter compared to the outside diameter of the longitudinally central body part of the tool 100. The central body part 102 of the expander tool 100 shown in FIG. 1 has three recesses 114, each holding a respective roller 116. Each of the recesses 114 has parallel sides and extends radially from a radially perforated tubular core (not shown) of the tool 100. Each of the mutually identical rollers 116 is somewhat cylindrical and barreled. Each of the rollers 116 is mounted by means of an axle 118 at each end of the respective roller 116 and the axles are mounted in slidable pistons 120. The rollers 116 are arranged for rotation about a respective rotational axis that is parallel to the longitudinal axis of the tool 100 and radially offset therefrom at 120-degree mutual circumferential separations around the central body 102. The axles 118 are formed as integral end members of the rollers 116, with the pistons 120 being radially slidable, one piston 120 being slidably sealed within each radially extended recess 114. The inner end of each piston 120 is exposed to the pressure of fluid within the hollow core of the tool 100 by way of the radial perforations in the tubular core. In this manner, pressurized fluid provided from the surface of the well, via a working string 310, can actuate the pistons 120 and cause them to extend outward whereby the rollers 116 contact the inner surface of a tubular to be expanded.

[0007] In one example of utilizing an expander tool, a new section of liner is run into the wellbore using a run-in string. As the assembly reaches that depth in the wellbore where the liner is to be hung, the new liner is cemented in place. Before the cement sets, an expander tool is actuated and the liner is expanded into contact with the existing casing therearound. By rotating the expander tool in place, the new lower string of casing can be fixed onto the previous upper string of casing, and the annular area between the two tubulars is sealed.

[0008] Galling takes place during expansion due to friction between the outside surface of an outwardly extended roller and an inside surface of the tubular being expanded. Friction between the surfaces increases the amount of torque needed at the surface of the well to rotate the expansion tool in the wellbore and complete the expansion process. Increased friction causes galling of the contacting surfaces leading to even greater friction and less efficiency of the expansion tool.

[0009] In order to reduce friction and prevent galling in a wellbore, lubricants have been used on threads and on surfaces between moving parts, like the rollers of expander tools and tubulars to be expanded. Lubricants have included grease and oil. Sometimes, soft metals such as copper, lead, zinc, or tin are added to the material making up contacting surfaces. The reasons for adding the soft metals are two fold. First, the soft metals provide a barrier that prevents galling and second, they deform under pressure and act as a lubricant. While these solutions reduce friction and the likelihood of galling, they are not completely effective.

[0010] There is a need, therefore, for a method and apparatus to reduce the friction encountered during the operation of a downhole tool that operates by contacting other surfaces. There is a further need for a method and apparatus for preventing galling created by friction between a downhole tool and other surfaces.

SUMMARY OF THE INVENTION

[0011] The present invention provides methods and apparatus for reducing friction and preventing galling between surfaces in a wellbore. Preferably, one or both of the contact surfaces are coated with a material having a spherical structure. In one aspect of the invention, a titanium carbide coating is placed between the roller of an expander tool and the surface of the tubular to be expanded in order to reduce friction and prevent galling.

[0012] In another aspect, the present invention provides a method for expanding a tubular in a wellbore. Initially, a tubular is disposed in the wellbore. The tubular is then expanded using an expander tool. The expander tool or the expanded area of the tubular include a coating of titanium carbide to prevent galling of the components. Furthermore, the coating reduces the friction forces between the tool and the tubular, thereby increasing efficiency.

[0013] In another aspect still, the present invention provides a method for lubricating two contacting surfaces in a wellbore. The method includes depositing a layer of titanium carbide on a first surface and causing the first surface to contact a second surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

[0015] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0016]FIG. 1 is an exploded view of an exemplary expander tool.

[0017]FIG. 2 is a partial section view of a tubular in a wellbore showing an expander tool attached to a working string also disposed within the tubular.

[0018]FIG. 3 is a partial section view of the partially expanded tubular of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] The aspects of the present invention are related to a downhole tool with a coating of carbide material having a spherical structure to reduce friction and prevent galling between two contacting surfaces.

[0020] In one aspect, titanium carbide (“TiC”) is coated on the exterior surfaces of an expander tool. The physical properties of titanium carbide make it one of the hardest and most durable materials. Additionally, titanium carbide has a generally spherical grain structure when viewed under a microscope. It must be noted that the term “spherical” encompasses a structure that is “multi-faceted”. These properties make titanium carbide a prime candidate for use as a lubricant to reduce friction.

[0021] Titanium carbide may be coated on a surface using any suitable method known to a person of ordinary skill in the art. For example, the titanium carbide coating may be deposited by physical vapor deposition, or sputtering. Using sputtering, the titanium carbide may be arranged as a target within a vacuum chamber in spaced relation to a surface to be coated. The surface may be positioned proximate a grounded electrode, and the target positioned proximate a conductive electrode. The chamber is back-filled with a gas at low pressure and a source of potential is applied to the electrodes. The potential source serves both to produce a plasma of the gas between the spaced electrodes and to attract the gas ions to the target. The potential causes the gas ions to bombard the target and break or knock off titanium carbide atoms or molecules from the target. These atoms or molecules settle on the surface and form a layer of titanium carbide. In another embodiment, the titanium carbide coating may be applied using a chemical vapor deposition process. It is understood that other deposition methods known to a person of ordinary skill in the art may also be used without deviating from aspects of the present invention.

[0022]FIG. 2 is a partial section view of a tubular 200 in a wellbore 300. The tubular 200 is disposed coaxially within the casing 400. An expander tool 100 is attached to a working string 310 and visible within the tubular 200. Preferably, the tubular 200 is run into the wellbore 300 with the expander tool 100 disposed therein. The working string 310 extends below the expander tool 100 to facilitate cementing of the tubular 200 in the wellbore 300 prior to expansion of the tubular 200 into the casing 400. A remote connection (not shown) between the working, or run-in, string 310 and the tubular 200 temporarily connects the tubular 200 to the run-in string 310 and supports the weight of the tubular 200. For example, the temporary connection may be a collett (not shown), and the tubular 200 may be a string of casing.

[0023]FIG. 2 depicts the expander tool 100 with the rollers 116 retracted, so that the expander tool 100 may be easily moved within the tubular 200 and placed in the desired location for expansion of the tubular 200. Hydraulic fluid (not shown) is pumped from the surface to the expander tool 100 through the working string 310. When the expander tool 100 has been located at the desired depth, hydraulic pressure is used to actuate the pistons (not shown) and to extend the rollers 116 so that they may contact the inner surface of the tubular 200, thereby expanding the tubular 200.

[0024] In one embodiment, the contact surfaces of the rollers 116 of the expander tool 100 may be coated with titanium carbide 150. FIG. 3 is a partial section view of the tubular 200 partially expanded by the expander tool 100. At a given pressure, the pistons (not shown) in the expander tool 100 are actuated and the rollers 116 are extended until they contact the inside surface of the tubular 200. The rollers 116 of the expander tool 100 are further extended until the rollers 116 plastically deform the tubular 200 into a state of permanent expansion. The working string 310 and the expander tool 100 are rotated during the expansion process, and the tubular 200 is expanded until the tubular's outer surface contacts the inner surface of the casing 400. The working string 310 and expander tool 100 are then translated within the tubular 200 until the desired length of the tubular 200 has been expanded.

[0025] It is believed that the titanium carbide coating 150 provides a lubricant like effect between the rollers 116 and the tubular 200. As the expander tool 100 is rotated against the tubular 200, the spherical grain structure of the titanium carbide 150 facilitates the relative movement between the contact surfaces. Consequently, less torque is needed to overcome the friction between the rollers 116 and the tubular 200. It is further believed that the titanium carbide coating 150, because it reduces friction, may also prevent galling of surfaces. The result is a more efficient expansion of the tubular 200. It must be noted that the either the rollers 116 or the tubular 200, or both may be coated with the titanium carbide 150. Moreover, the titanium carbide coating 150 may be applied to other downhole tools to reduce friction. Additionally, the components of the expander tool 100, such as the rotors, bearings, and the shaft, may also be coated with titanium carbide 150 to reduce friction.

[0026] In another aspect, the titanium carbide coating may be used with a swedge shaped mandrel or a cone to increase the diameter of a tubular without the use of an expander tool having extendable rollers. In one example, a cone-shaped member is run into a wellbore and into contact with the upper end of a tubular to be expanded. In another example, the cone can be run into the wellbore on a lower end of a tubular run in string. The cone is designed with an outer diameter greater than the inner diameter of the unexpanded tubular. The outer surface of the cone may be coated with titanium carbide to reduce friction and prevent galling as the cone is urged into the tubular. Alternatively, an inner surface of the tubular in contact with the cone may be coated with titanium carbide, or both contacting surfaces may be coated with the same.

[0027] With the coating in place, it is believed that the amount of friction generated during the process of passing the cone into the tubular will be significantly reduced. Additionally, any galling between the surface of the cone and the inner surface of the tubular will be minimized. The reduction in surface damage to the tubular wall can be important if the surface characteristics of the tubular after expansion are critical. In one example, a tubular is enlarged in situ in order to form a polish bore receptacle (“PBR”) therein. The use of a coating of titanium carbide according to the present invention will help ensure that the PBR has surface characteristics according to specification.

[0028] While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

I claim:
 1. A method for lubricating two contacting surfaces in a wellbore, comprising: depositing a layer of titanium carbide on a first surface; and causing the first surface to contact a second surface.
 2. The method of claim 1, wherein the second surface is coated with titanium carbide.
 3. A method of lubricating a surface of a downhole component, comprising: placing a layer of titanium carbide on the surface, whereby the surface will contact another surface in a wellbore and create friction therebetween.
 4. An expander tool for expanding a tubular, the tool comprising: a body having a bore longitudinally formed therethrough; and one or more roller members radially extendable from the body, wherein a portion of the one or more roller members include a coating comprising titanium carbide.
 5. The expander tool of claim 4, wherein the one or more rollers extend due to fluid pressure applied from the bore to a piston surface formed on a roller housing.
 6. The expander tool of claim 4, wherein an inner surface of the tubular comprises the titanium carbide coating.
 7. The expander tool of claim 6, wherein the inner surface is expanded by the expander tool.
 8. The expander tool of claim 4, wherein the titanium carbide is deposited by sputtering.
 9. A method for expanding a first tubular into a second tubular in a wellbore, the first tubular and second tubular each having a top portion and a bottom portion, comprising: positioning the first tubular within the wellbore; running the second tubular to a selected depth within the wellbore such that the top portion of the second tubular overlaps with the bottom portion of the first tubular, wherein an inner surface of the top portion of the second tubular comprise a titanium carbide coating; and expanding the top portion of the second tubular using an expander tool.
 10. The method of claim 9, wherein the expander tool comprises: a body having a bore longitudinally formed therein; and one or more roller members radially extendable from the body.
 11. The method of claim 10, wherein the one or more roller members comprise a titanium carbide coating.
 12. The method of claim 10, wherein the one or more rollers extend due to fluid pressure applied from the bore to a piston surface formed on a roller housing.
 13. The method of claim 9, wherein the first tubular and the second tubular each define a string of casing.
 14. The method of claim 9, wherein the expander tool comprises a cone shaped portion.
 15. The method of claim 14, wherein the cone shaped portion includes a titanium carbide coating.
 16. A method for expanding a tubular in a wellbore, comprising: positioning the tubular within the wellbore; placing an expander tool within the tubular at a location adjacent a portion of the tubular to be expanded, wherein at least one of the portion of the tubular and a portion of the expander tool comprise a titanium carbide coating disposed thereupon; and expanding the tubular using the expander tool.
 17. The method of claim 16, wherein the expander tool is a cone-shaped member movable independently within the tubular and having an outer diameter larger than an inside diameter of the unexpanded tubular.
 18. The method of claim 16, wherein the expander tool includes at least one radially extendable member that is extendable with the application of fluid pressure to a backside thereof. 